JPH03267971A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the scattering of a toner by setting a potential controlling means to impress bias different from transfer bias in polarity on a transfer material at a position before a transfer part. CONSTITUTION:A pair of guides are arranged along the travelling direction of a transfer material at the downstream side of a pair of resist rolls 10, 11 and an opening covering the width of the transfer material is pierced in the lower guide 8a. An electrifier 18 is set under the opening, a DC power source 19 is connected to the electrifier 18, in such a case, polarities of photosensitive body 1 and toner, etc., are the same polarity as well-known device and negative bias voltage is impressed on the electrifier 18. Even when the transfer material approaches a transfer part, the scattering of a toner from a photosensitive body 1 is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Object of the Invention (Field of Industrial Application) The present invention relates to an image forming apparatus that uses an electrostatic transfer process, such as an electrostatic copying machine and a printer thereof.

(Prior Art and Issues to be Solved) In the well-known image forming apparatus as described above, the transfer material reaches the transfer site formed as a nip between the moving image carrier and the transfer roller that presses against it. There is a problem in that the toner on the surface of the image bearing member is electrostatically attracted to the transfer material at a position before the transfer, resulting in a so-called scattering phenomenon, which causes deterioration in image quality.

This will be briefly explained using Figure \.

In the figure, a cylindrical image carrier (hereinafter referred to as a photoconductor) extends perpendicular to the plane of the paper and rotates in the direction of the arrow in the figure.
1 is uniformly charged by a charging means such as a charger (not shown), and the charged surface is irradiated with an image signal such as an image-modulated laser beam, and the potential of that portion is attenuated. An electrostatic latent image is formed.

Toner charged to a predetermined polarity is supplied to this latent image from a developing device (also not shown) to form a toner image, and as the photoreceptor 1 rotates, the toner image comes into pressure contact with the photoreceptor 1. When the toner image reaches a transfer site formed as a pressure nip portion of the transfer roller 5, a transfer bias is applied to the transfer roller 5, and the toner image is transferred to the transfer material.

Thereafter, the transfer material carrying the toner image is separated from the photoreceptor 1, passes through the fixing section 7 via the conveyance path 12, fixes and fixes the toner image on the transfer material, and is discharged from the apparatus.

The transfer material is taken out one by one by a paper feed roller 3 from a cassette 14 serving as a storage section, passes through a conveyance path 12, and is guided by a pair of registration rollers 10 and 11 in accordance with the toner image on the surface of the photoreceptor 1. 8.9 to the aforementioned transcription site.

In the case of this device, the surface of the photoreceptor 1 is initially negatively charged, and negatively charged toner is supplied to this to form a toner image by reversal development.
It is assumed that this toner image is transferred to the transfer material by the action of the transfer roller 5 to which a bias of positive polarity is applied.

The resistance value of the transfer roller 5 has a volume resistance of 104 to 10'Ω.
Low resistance of about cm, volume resistance is 108~109Ω
cm medium resistance type can be used, and the transfer bias is 500 to 800 ■ in the former case, and 3 to 4 K in the latter case.
V is preferred.

The above-mentioned scattering in such a device will be explained.

As shown in FIG. 3, the transfer material stored in the cassette 14 is taken out from the cassette by friction with the paper feed roller 3, and reaches the pair of registration rollers 10 and 11 while sliding against the conveyance guide 12. It receives friction from the surface and reaches the transcription site.

In general, paper feed roller 3, registration roller pair 10.11
etc., so that a suitable frictional force acts between the transfer material and the transfer material.
The surface is usually a rubber surface, and due to the friction between the paper, which is mostly used as a transfer material, and the rubber, the paper, which is the transfer material, becomes positively charged, and the rubber becomes negatively charged.

Therefore, if the surface of the photoreceptor, toner, etc. have the above-mentioned polarity, and the potential of the paper used as the transfer material is high (sometimes exceeding 2KV), the potential of the paper becomes high (sometimes exceeding 2KV), and The toner on the photoconductor side near the transfer material is attracted and adhered to the transfer material in an irregular manner, causing a scattering phenomenon and deterioration of image quality.

In the case of roller transfer, compared to the case of corona transfer, the area where the charge is applied to the transfer material during transfer is narrower, and the amount of charge given to the transfer material is also smaller. The quality of the image is significantly lower than in the case of .

In other words, even if the amount of charge is not a problem in the case of corona transfer, the image quality deteriorates in the case of roller transfer.

Transfer is based on the electric field formed by the transfer bias applied to the transfer roller, so a higher bias is required when using a medium resistance transfer roller than when using a low resistance transfer roller. In the latter case, the occurrence of scattering tends to be more pronounced due to the effects of both the electric field strength and the charged potential of the transfer material. In an image forming apparatus, the surface potential of the transfer material is set at a position before the transfer material reaches the transfer site.
It is an object of the present invention to provide an image forming apparatus that can prevent the toner from scattering by providing a means that prevents the toner from becoming high before it is sucked.

(2) Structure of the invention (technical means for solving the problem and its operation) In order to achieve the above object, the present invention provides a pressure nip portion between an image bearing member and a transfer roller that is pressed against the image bearing member in an image forming apparatus. In an image forming apparatus that performs transfer by passing a transfer material through a transfer site and applying a transfer bias to the transfer roller, a transfer bias having a polarity different from that of the transfer bias is applied at a position before the transfer material reaches the transfer site. The present invention is characterized in that it is provided with a control means that applies a bias to the transfer material and controls the potential of the transfer material to such a potential that the toner does not fly onto the transfer material.

With this configuration, it is possible to prevent toner from scattering from the photoreceptor side and adhering to the transfer material arriving at the transfer site, thereby preventing deterioration of image quality in the future.

(Description of Embodiment) FIG. 1 is a schematic side view of the main parts of an image forming apparatus showing an embodiment of the present invention, and its basic configuration and operation are the same as those shown in FIG. 8 above. , corresponding parts are shown with the same reference numerals, and a description thereof will be omitted.

In the illustrated apparatus, the lower guide 8a of the pair of guides arranged downstream of the registration roller pair 10. An opening is formed, and a charger 18 is disposed in the opening, and a DC power source 19 is connected to the charger 18. In this case, the polarity of the photoreceptor 1, toner, etc. is determined according to the known method. As in the case of the apparatus, the configuration is such that a negative bias voltage is applied to the charger 18.

With this configuration, when the transfer material 15 passes the position of the charger 18 in a positively charged state in the manner described above, the charger imparts a negative charge to the transfer material. Since the static electricity is removed by the photoreceptor, even if the transfer material approaches the transfer site, toner will not fly from the photoreceptor.

The charging voltage of the charger 18 may be set so that when the maximum amount of transfer material that can be passed is positively charged, it becomes a negative potential, at least near zero potential.

With this configuration, it is possible to prevent a situation in which the toner on the photoreceptor side forming a toner image flies onto the transfer material and deteriorates the image quality before the transfer material reaches the transfer site.

FIG. 2 shows another embodiment. In this case, an AC power source 21a and a DC power source 21b are combined into a charger 18 disposed at a transfer guide portion, and a bias voltage is applied from the power source 21 by superimposing both of them. is being applied.

By using such a charging means, the potential convergence property is improved and the surface potential of the transfer material can be easily controlled, and by adjusting the DC component, the potential of the transfer material is made higher than the surface potential of the photoreceptor, thereby preventing toner scattering. The presence of the alternating current component makes it possible to widen the latitude with respect to the type, thickness, etc. of the transfer material.

FIG. 3 shows another embodiment of the present invention, in which a grid 23 is provided on a charger 18 disposed at a transfer guide site, and a grid bias is applied by a power source 24.

With this configuration, the transfer material surface potential can be converged to a predetermined value without using an AC power supply, and the potential can be appropriately controlled by changing the grid bias.

FIG. 4 shows yet another embodiment, in which a conductive brush 22 is disposed at the tip of the transfer guide 8b so as to come into contact with the transfer material passing therethrough. A bias (negative polarity in this case) is applied to the brush by a power source 27.

Since the transfer material is negatively charged as it slides past the brush, toner scattering can be reduced.

This device is particularly suitable for small-sized image forming apparatuses where space is limited, and the bias applied to the brush may be approximately 0 to -3 Kv.

Instead of the brush in the above device, a plate member 30 made of stainless steel and having a serrated edge and having a thickness of about 0.2 mm, for example, as shown in FIG. 5, may be used.

By arranging such a member 30 at the position of the brush in the device shown in FIG. 4 so as to be close to the passing transfer material and applying a bias, the same effect as in the device described above can be obtained. It will be done.

In this case, there is no need to bring the plate member 30 into direct contact with the transfer material, which is advantageous from the viewpoint of durability.

FIG. 6 shows yet another embodiment of the present invention.

In this device, a conductive roller 28 has a conductive pile 29 planted in an opening formed in the transfer guide 8a.
It is assumed that a bias voltage is applied by the power supply 27 to the pile, and the transfer material advances while rubbing against the pile.

The roller 28 may rotate in either forward or reverse direction as long as it has an appropriate relative speed to the transfer material.

With this configuration, by appropriately setting the traveling speed of the transfer material and the pile that comes into contact with the transfer material, it is possible to remove static electricity from the transfer material more efficiently than with the above-mentioned brush.

In the apparatus described above, the self-discharge members such as the brush 22, the plate member 30, and the roller 28 are arranged below the transfer material in the drawing, but these members can be arranged above the transfer material as needed. Alternatively, it is of course possible to arrange them both above and below.

FIG. 7 shows another embodiment of the present invention, in which a pair of bias rollers 26 are disposed in pressure contact with each other in the openings formed in the transfer guides 8a and 9a, and the advancing transfer material is transferred to these bias rollers. At the same time, a bias is applied to the pair of rollers by a power source 27.

As the bias roller 26, a conductive rubber roller, a metal roller, or the like having appropriate elasticity can be used.

With this configuration, the transferred and charged transfer material undergoes charge separation or injection, and the surface mold 2 is controlled, thereby reducing toner scattering when approaching the transfer site.

Generally, if the transfer material is configured to pass through registration rollers and reach the transfer site, when the transfer material passes through the rollers, there is a risk that transfer misalignment will occur at the transfer site and the image will be distorted. On the downstream side of the registration rollers, there is a pair of rollers for receiving the transfer material, and by constructing these rollers from a foamed material having a hardness of about 20 DEG (Asker-C), the above-mentioned problems can be solved.

Note that it is also possible to simplify the configuration by applying a bias to the pair of registration rollers to simultaneously perform transfer material conveyance and charge control.

In the above embodiments, an apparatus employing a reversal development method has been described, but it goes without saying that the present invention is not limited to this, and can also be applied to regular development.

(3) As described in detail, according to the present invention, the charged transfer material is reliably transferred before the transfer material reaches the transfer site formed by the image carrier and the transfer roller that is in pressure contact with the image carrier. Since the potential can be controlled to a level that can prevent the toner from flying off, it is possible to prevent the image from being disturbed by the toner scattering at the front position of the transfer portion, and to obtain good transfer performance.

[Brief explanation of drawings]

FIG. 1 is a schematic side view of main parts of an image forming apparatus showing an embodiment of the present invention, and FIGS. 2 to 4 and FIGS. 6 and 7 are main parts showing other embodiments of the invention. FIG. 5 is a perspective view showing an example of a self-discharge member, and FIG. 8 is a schematic side view of main parts showing the configuration of a known image forming apparatus. 1 ・ ・ a19 Resist charger, power supply, 2 U. - Photoreceptor, 5... Transfer roller, 8.9a... Transfer guide, 10.11... Roller, 15... Transfer material, 1
8...19.21.24.27...Bias 2...
・Brush, 28... Static elimination row 1st section 2nd figure

Claims (4)

[Claims] (1) In an image forming apparatus in which a transfer material is passed through a transfer site that is a pressure nip between an image carrier and a transfer roller that is in pressure contact with the image carrier, and a transfer bias is applied to the transfer roller to perform transfer, the transfer material is transferred to the transfer site. An image forming apparatus comprising: a potential control means for applying a bias having a polarity different from the transfer bias to a transfer material at a position before the transfer material reaches the transfer material. (2) The image forming apparatus according to claim 1, wherein the potential control means for controlling the potential of the transfer material is a charger. (3) The image forming apparatus according to claim 1, wherein the potential control means for controlling the potential of the transfer material is a self-discharge member. (4) The image forming apparatus according to claim 1, wherein the potential control means for controlling the potential of the transfer material is a roller.